UPDATE 07/09 – 14:26 UTC : Tremor has continued at El Hierro since the start of seismicity in July. Between the 30th August and 3rd September seismic events were high at ~200 to 250 a day. However, since then there have been less than 100 events a day. GPS stations are now in place around the volcano. On the 24th of August Eruptions Blog and @Teideano reported an uplift of ~1 cm. There has been no uplift (inflation – to my knowledge) reported recently.It seems that magma is still moving beneath El Hierro and may continue for a while to come yet. So keep watching.Up to date info is available at Actualidad Volcánica de Canarias.

UPDATE 05/08 – 21:09 :Earthquake events are continuing underneath El Hierro, with the majority of events between 8 and 15 km in depth, and as shallow as 2 km (+/- 0.5) with an average of around 11.5 km. As of yet, there are still NO other additional signs of an eruption, an increase in gas (which has been detected) or any change to deformation signals.
In a post of the Eruptions blog by Erik Klemetti, the situation at El Hierro is described in detail. For the moment it is still to early to tell what will happen, so keep watching.

Original text
Recently El Hierro volcano of the Canary Islands has been experiencing a seismic swarm beneath it, which as of yesterday reached to over 700 events.

Most of these events have been at Magnitudes of around 2 (+/-0.5) and are clustered beneath El Hierro whilst the depths of these earthquakes have been roughly between 9 and 16 km for the most part, with the exception of a few shallower and deeper quakes, the shallowest of which has been around 4 km (as of 27/04/11 8am GMT for the plotted data below) but as shallow as 1 km following this.
If we look at these earthquakes in two plots here http://www.volcano-blog.com/hierro.html we can see the clustering of these earthquakes is mainly confined to an oval area at 10 km depth.

El Hierro is a broadly basaltic volcano which might have been active in 1793 although this is uncertain.

So the big question is, what’s happening here?
It is possible that there is magma on the move at depth, perhaps moving into a magma chamber.
Does this mean that there will be an eruption? Maybe, maybe not.
The majority of magma intrusions do not reach the surface, and as has been seen elsewhere, in the past, activity can cease at anytime.

As of yet (to my knowledge) there have been no other signs of moving magma at the surface such as ground deformation or increased gas emission, although GPS antenna have been set up by officials at the Canary Islands.
For now it is too early to tell what (if anything) will happen, so keep watching.
If you would like to follow these earthquakes in more detail or look at the raw data, visit here .

El Hierro Volcano Information :
The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive Hierro shield volcano is truncated by a large NW-facing escarpment formed as a result of gravitational collapse of El Golfo volcano about 130,000 years ago. The steep-sided 1500-m-high scarp towers above a low lava platform bordering 12-km-wide El Golfo Bay, and three other large submarine landslide deposits occur to the SW and SE. Three prominent rifts oriented NW, NE, and south at 120 degree angles form prominent topographic ridges. The subaerial portion of the volcano consists of flat-lying Quaternary basaltic and trachybasaltic lava flows and tuffs capped by numerous young cinder cones and lava flows. Holocene cones and flows are found both on the outer flanks and in the El Golfo depression. Hierro contains the greatest concentration of young vents in the Canary Islands. Uncertainty surrounds the report of an historical eruption in 1793.

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Can anyone tell me if there is any information about what might be going on below La Palma Island. There have been an increase in siesmic activity there according to the IGN charts, tremors which seem to be more like those of volcanic activity rather than tectonic. http://www.01.ign.es/ign/layoutIn/volcaSenalesAyerHoy.do#